This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In order to meet consumer and industrial demand for natural resources, companies often invest significant amounts of time and money in finding and extracting oil, natural gas, and other subterranean resources from the earth. Particularly, once a desired subterranean resource such as oil or natural gas is discovered, drilling and production systems are often employed to access and extract the resource. These systems may be located onshore or offshore depending on the location of a desired resource. Further, such systems generally include a wellhead assembly through which the resource is extracted. These wellhead assemblies may include a wide variety of components, such as various casings, valves, fluid conduits, and the like, that control drilling or extraction operations.
More particularly, wellhead assemblies often include a blowout preventer, such as a ram-type blowout preventer that uses one or more pairs of opposing rams that press against one another to restrict flow of fluid through the blowout preventer. Typical blowout preventers are used as a large specialized valve or similar mechanical device that seal, control, and monitor oil and gas wells. The two categories of blowout preventers that are most prevalent are ram blowout preventers and annular blowout preventers. Multiple blowout preventers are frequently assembled in a stack. The stack typically includes both types of blowout preventers, usually with at least one annular blowout preventer stacked above several ram blowout preventers. The ram units in ram blowout preventers allow for both the shearing of the drill pipe and the sealing of the blowout preventer. The annular blowout preventer seals around the drill pipe thereby sealing the annulus surrounding the drill pipe. A blowout preventer or blowout preventer stack may be secured to a wellhead directly or indirectly, and may provide a safe means for sealing the well in the event the primary pressure control system has been compromised.
Blowout preventers are typically coupled with other components, in a stack or otherwise, by bolted upper and lower end connections. The lower end connection of the blowout preventer is typically a flange connection which is bolted to an upper end of the component directly below. The upper end connection of the blowout preventer is typically a non-flange connection which is bolted to a lower end of the component directly above. The upper end connection of the blowout preventer comprises one or more ram cavities which intersect a longitudinal bore of the blowout preventer.
One or more fasteners on the upper end connection of the blowout preventer are located over the ram cavities. Other bolts are not located over the ram cavities. The bolts over the ram cavities can move up or down when under load because of the elastic deflection of the body above the ram cavities. The other bolts cannot move up or down as much. As a result, the bolts over the ram cavities experience lower stresses than the bolts not over the ram cavities, i.e., loading on the upper end connection bolts is uneven. Accordingly, a blowout preventer end connection providing for more even loading is desirable.